Could you please check the grammar in these sentences? Thanks.

It was clearly her, right from the start.
These are they, if I'm not mistaken.
It always appeared to be them whenever there was trouble.
The penalty against them brought coach Henson and I great satisfaction.
This should be them.
This is him, so guard him carefully.
Her favorite targets are Donna and I.
The only remaining customers are the Smiths and I.

It was she , not her. You wouldn't say Her was it.

You would not say It brought I.

You would not say Them would be this.

nor would you say Him is this

If there is a "to be" verb, then reverse the predicate pronoun and the subject to see if you have made a correct choice.